1. Field of the Invention
The present invention relates generally to a magnetic bearing device and, more particularly, to a magnetic bearing device in which the need for detection of and control of the position of a rotational member in the axial direction is eliminated to reduce the number of component parts, and which, therefore, can be smaller in size and can have lower manufacturing cost and lower power consumption.
2. Description of the Related Art
FIG. 5 illustrates an example of a conventional magnetic bearing device 10 of a five axes control type. An upper radial electromagnet 1 in the arrangement shown in FIG. 5 is capable of adjusting the position in the radial direction (hereinafter referred to simply as xe2x80x9cradial positionxe2x80x9d) of an upper portion of an inner rotor 3 with an adjustment meter or the like (not shown) based on a radial position detected by an upper radial position detection sensor 2. On the other hand, a lower radial electromagnet 5 is capable of adjusting the radial position of a lower portion of the inner rotor 3 with an adjustment meter or the like (not shown) based on a radial position detected by a lower radial position detection sensor 6.
A motor 7 is provided between the upper radial electromagnet 1 and the lower radial electromagnet 5 to cause the inner rotor 3 to rotate at a high speed in a state of floating by magnetic force. A disk 9 is fixed to a portion of the inner rotor 3 below the lower radial position detection sensor 6. The disk 9 is attracted upward by an upper axial electromagnet 11a and is attracted downward by a lower axial electromagnet 11b. 
An axial sensor 13 is provided in a lower portion of a cylindrical casing 15 so as to face the lower end of the inner rotor 3. The position in the axial direction (hereinafter referred to simply as xe2x80x9caxial positionxe2x80x9d) of the inner rotor 3 can be adjusted by balancing the attractions of the upper and lower axial electromagnets 11a and 11b with an adjustment meter or the like on the basis of the axial position detected by the axial sensor 13.
In the above-described conventional magnetic bearing device 10, however, the axial sensor 13, the upper axial electromagnet 11a and the lower axial electromagnet 11b are required for supporting the rotor at the predetermined axial position.
The number of component parts of the magnetic bearing device 10 is thereby increased, so that it is difficult to reduce the manufacturing cost and size of the magnetic bearing device. Moreover, since electric power is consumed by the upper and lower axial electromagnets 11a and 11b, there is a limit to reduction of the power consumption.
The present invention has been made in view of the above-described problems of the conventional art, an object of the present invention is to provide a magnetic bearing device in which the need for detection of and control of the position of a rotating member in the axial direction is eliminated to reduce the number of component parts, and which, therefore, can be smaller in size and can have lower manufacturing cost and lower power consumption.
To achieve the above-described object, according to the present invention, there is provided a magnetic bearing device comprising: a rotational member floated and supported by magnetic force; at least one permanent magnet arranged on the rotational member; magnetic means for rotating the rotational member by magnetic fields generated through a core on which motor coils are formed, and which is spaced apart from the permanent magnet in the radial direction so as to form a predetermined gap therebetween; at least one set of radial position detection means for detecting the radial position and/or the inclination of the rotational member; and at least one set of radial position adjustment means for adjusting the radial position and/or the inclination of the rotational member based on the radial position and/or the inclination of detected by the radial position detection means. According to the present invention, the rotational member is supported at the desired axial position by axial direction components of magnetic attractions generated between the permanent magnet and the core.
The rotational member rotates in a state of floating by magnetic force. The rotational member comprises an inner rotor and an outer rotor. The magnetic bearing device is assumed to comprise an electric motor and a generator capable of floating a rotational member by magnetic force. The rotational member is provided with at least one permanent magnet. The core on which the motor coils constituting the magnetic means are formed is spaced apart from the permanent magnet so as to form a predetermined gap therebetween. The rotational member is rotated by magnetic attraction forces generated between the permanent magnet and the magnetic means.
The radial position detection means detects the radial position and/or the inclination of the rotational member. The radial position adjustment means adjusts the radial position and/or the inclination of the rotational member based on the radial position and/or the inclination detected by the radial position detection means.
In the case of three axes control, a radial position control is formed by one set of radial position detection means and one set of radial position adjustment means. In the case of five axes control, a radial position control is formed by two sets of radial position detection means respectively provided in two places distanced apart from each other along the axial direction, and two sets of radial position adjustment means also provided in two places along the axial direction.
There is no particular limitation in the order in which the radial position detection means and the radial position adjustment means are arranged in the axial direction.
The rotational member is supported at the desired axial position by axial direction components of magnetic attractions generated between the permanent magnet and the core.
As described above, the need for detection of and control of the position of the rotational member in the axial direction can be eliminated. Accordingly, the number of component parts can be reduced, and the magnetic bearing device can be small in size and can have low manufacturing cost and low power consumption.